It is the purpose of the proposed research to explore and develop methods for utilizing III Indium-labeled platelets to identify and evaluate the presence, the location, and the extent of arterial and venous thrombotic events in vivo. Serial whole body scintiscans may assist in establishing the diagnosis, the natural course, and the effect of therapy upon thrombotic disease states with this new, safe, noninvasive and potentially quantitative technique. The specific areas addressed were chosen for investigation because these are important health care problems. The true incidence of thrombosis and thromboembolism following routine and long-term catheterization is at present unknown, and will be studied. The relative thrombogenic properties of various catheter materials will be compared as well as methods claimed to reduce this propensity. Angiographic jet trauma will also be examined. Experimentally induced myocardial infarction will be studied with the proposed technique and will be compared with 99mTc-pyrophosphate and 201TI methods. Human studies are proposed in selected patient groups: cardiac patients with coronary bypass grafts and prostheses, patients with acute pulmonary embolism, deep vein thrombosis, and acute myocardial infarctions. The effect of antiplatelet drugs on platelet localization will also be examined.